Step 3: Pick out 3 cups bite-size cauliflower florets and combine them with the broccoli romanesco and broccoli rabe on another rimmed baking sheet (set aside any broccoli rabe flowers).

Step 4: Chop the remaining cauliflower and set aside. Drizzle 1 tbsp of the oil and sprinkle 1 tsp of the salt over each baking sheet.

Step 5: Roast the vegetables, stirring often, until golden brown and tender when pierced with a fork, about 20 minutes for the mixed vegetables and 25 minutes for the potatoes.

Step 6: Meanwhile, heat the remaining 1 tbsp oil in a large pot over medium heat. Add the garlic and onion and cook, stirring often, until translucent, about 5 minutes. Add the remaining potatoes, the chopped cauliflower, and 6 cups water and bring to a simmer. Cover and cook until the vegetables are tender, about 15 minutes. Remove from the heat and let cool slightly.

Step 7: Working in batches, ladle about 2 cups of the liquid and vegetables into a blender and process until smooth. Pour through a fine-mesh strainer set over a large bowl, using the back of the ladle to push the soup through.

Step 8: Pour the purée back into the pot and bring to a simmer over low heat. Stir in the cream and the remaining 1 tsp salt, then add the roasted vegetables and heat through.

Step 9: Serve the chowder in deep soup bowls, drizzled with oil and sprinkled with chopped rosemary and broccoli rabe and rosemary flowers.